Multi-cusped postcanine teeth are associated with zooplankton feeding in phocid seals

Abstract

Tooth morphologies often reflect diet in animals. Among marine mammals, a well-known example is the krill-feeding crabeater seal Lobodon carcinophaga, in which complex, comb-like postcanine teeth function as a sieve by retaining krill inside the mouth while expelling water. However, information on tooth morphology and function is scarce for other seal species. A recent bio-logging study found that Baikal seals Pusa sibirica feed on tiny pelagic amphipods at remarkably high rates with highly multi-cusped postcanine teeth, highlighting the need for comparative analyses on tooth morphologies and diets in phocid seals. Here, we quantified postcanine tooth morphology for 13 seal species based on museum skull specimens, with a particular focus on Baikal seals and their related species (genera Pusa and Phoca). Pusa species, including Baikal seals, had more specialized multi-cusped postcanine teeth than Phoca species, reflecting higher zooplankton proportions in their diets. Postcanine teeth of Baikal seals exhibited the highest degree of specialization among Pusa, even when the effect of age-related wear was controlled for. This result agrees with the highest zooplankton preference in this species. Further, we found a strong positive correlation between the degree of specialization in postcanine teeth and zooplankton reliance across phocid seal species. Our findings indicate that the functional role of multi-cusped postcanine teeth as a sieve is not limited to crabeater seals but prevails in many phocid seals feeding on zooplankton.